Regenerative air heater with reversible drive

ABSTRACT

A heat exchanger of the regenerative type wherein combustion gases pass in contact with heat exchange surface and gives off heat to the surface. The surface is rotatably mounted so as to come into contact first with a primary air stream to give off heat thereto, and upon further rotation it comes into contact with a secondary air stream to also impart heat to it. A reversible drive is provided for the rotatably mounted heat exchange surface so that when desired the secondary air stream first encounters the heat exchange surface in its hottest state, and upon further rotation, the primary air stream is heated to a lesser extent.

United States Patent [19] Harris et al.

[ Mar. 26, 1974 REGENERATIVE AIR HEATER WITH REVERSIBLE DRIVE [75] Inventors: David A. Harris, Simsbury; Henry E. Burbach, Avon; Joseph G. Singer, Bloomfield, all of Conn.

[73] Assignee: Combustion Engineering, Inc.,

Windsor, Conn.

[22] Filed: Dec. 30, 1971 [21] Appl. No.: 213,860

[52] US. Cl 165/7, 110/56, 165/10 [51] Int. Cl. F28d 19/00 [58] Field of Search 165/7, 10; 110/56 [56] References Cited UNITED STATES PATENTS 2,337,907 12/1943 Lundstrom 165/7 2,769,619 ll/1956 Juhasz 165/7 Primary Examiner-Albert W. Davis, Jr.

Attorney, Agent, or Firm-Robert L. Olson [5 7] ABSTRACT A heat exchanger of the regenerative type wherein combustion gases pass in contact with heat exchange surface and gives off heat to the surface. The surface is rotatably mounted so as to come into contact first with a primary air stream to give off heat thereto, and upon further rotation it comes into contact with a secondary air stream to also impart heat to it. A reversible drive is provided for the rotatably mounted heat exchange surface so that when desired the secondary air stream first encounters the heat exchange surface in its hottest state, and upon further rotation, the primary air stream is heated to a lesser extent.

2 Claims, 4 Drawing Figures PAIENIEBunzs 1914 3.799242 sum 2 or 2 INVENTOKI VAV/D A- HARE/5 HENRY E EUQBACH JOSEPH 6- SINGER A TT'ORNE Y REGENERATIVE AIR HEATER WITH REVERSIBLE DRIVE BACKGROUND OF THE INVENTION The invention is directed to a tri-sector type of rotary regenerative air heater where combustion gases are used for heating both the primary combustion air and the secondary combustion air for a steam generator using coal as the fuel. In such systems, the primary air is generally used for drying the coal in a pulverizing mill, and then the coal is pneumatically transported to the furnace in the primary air stream. When pulverizing coal of a given moisture content, and in given quantities, a given amount of primary air at a definite temperature will result in optimum efficiency of a unit. This is how the initial size of a rotary regenerative air heater is determined. Using atmospheric air to temper the hot primary air leaving the air preheater is one way of getting small temperature changes if they are needed, even though it will result in somewhat less efficiency of the system because of changes in the total heat recovery. Ifa different coal is to be burned in a unit at a later time which has a substantially smaller moisture content, problems are encountered in lowering the primary air temperature without also greatly decreasing the efficiency of the system. The converse is also true, if coal with a greater moisture content is to be later burned.

SUMMARY OF THE INVENTION The rotary regenerative air heater of the present invention utilizes a rotatable heater containing heat exchange surface which is first heated by a stream of combustion gases in a first section of the heater, the rotatable surface then heats a stream of primary combustion air upon further rotation into a second section of the heater and finally heats a stream of secondary combustion air upon still further rotation into a third sectorial section of the heater. A reversible drive is provided for the rotary air heater to permit the secondary air to be heated to a greater or lesser extent than the primary air by reversing the direction of the rotation of the air heater.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a side view of a steam generator incorporating the novel regenerative air preheater of the invention;

FIG. 2 is an enlarged view of the air preheater shown in FIG. 1;

FIG. 3 is a sectional view of the air preheater taken on lines 3-3 of FIG. 2; and

FIG. 4 is a sectional view of the air preheater taken on lines 4-4 of FIG. 2.

DESCRIPTION OF THE PREFERRED EMBODIMENT Looking now to FIG. 1 of the drawings, 10 designates the furnace of a steam generator, where pulverized coal, introduced through inlet ports 12, is burned. The pulverized coal is conveyed to the furnace in a stream of primary air from the primary air fan 31 through coal pipes 20 from mill 18, where the coal is not only pulver ized, but is also dried. Secondary combustion air is introduced to the furnace I through inlet ports 16. Hot air is supplied through duct 34 to the pulverizing mill l8, and to duct 22, leading to ports 16, from the rotary regenerative air pre-heater 24. The primary air is supplied to preheater 24 by fan 31 through duct 40. These air streams are heated by combustion gases exhausted from the steam generator through duct 26. After giving up heat in air preheater 24, the combustion gases are discharged to the atmosphere through duct 28. Cool atmospheric air can be added to the primary hot air exiting from the air preheater 24 through dampered duct 23 when small temperature changes in the primary air is needed.

Secondary air is supplied to the air preheater by forced draft fan 30 through duct 32. On both the air outlet and air inlet side of the air preheater, the duct connections are arranged in a tri-sector form. As best seen in FIG. 4, the incoming combustion gas duct 26 has a first sectorial connecting portion 36. Proceeding in a clockwise direction, the primary air duct 34 has a second sectorial connecting portion 40. Proceeding further in the clockwise direction, secondary air duct 22 has a third sectorial connecting portion 38. The three sectorial connections 36, 38 and 40 are separated by sector plates 37, 39 and 41. These sector plates are for the purpose of preventing intermixing of the various fluid streams to any great extent, as is well known in the rotary regenerative art. A similar arrangement is found on the combustion gas outlet side of preheater 24.

FIG. 3 shows the construction of the air heater. Mounted within a cylindrical housing 25 is a rotatable cylinder 27. Cylinder 27 is secured to and rotatable by means of rotor 42. A plurality of radial, imperforate plates 31 divide cylinder 27 into a series of equally sized flow passages. These passages are filled with any well-known heat exchange surface 33.

Looking now to FIG. 2, it can be seen that rotor 42 of the air heater 24 is rotatable in either direction by a reversible motor 44. Motor 44 is shown with contacts 46, 48, 50 and 52 connected to control energization and direction of rotation thereof. Motor 44 is shown as a three phase AC motor and clockwise rotation is effected by closing contacts46 and 52; while counterclockwise rotation is initiated and controlled by closure of contacts 48 and 50.

From the above, it can be seen that the heat exchange surface 33 (FIG. 3) is first heated by the combustion gases entering air preheater through sectorial connection 36 (FIG. 4). As the rotor 42 rotates the heat exchange surface 33 in a clockwise direction, the heat exchange surface 33 heats the primary air stream which exits from the air heater 24 through the sectorial connection 40. Upon further clockwise rotation, the heat exchange surface 33 also heats the secondary air stream exiting through sectorial connection 38. Since the heat exchange surface is hottest just as it rotates out of the combustion gas stream, the primary air is heated to a greater extent than the secondary air, when the air heater is rotated in a clockwise direction. If a coal having less moisture is to be burned at some later time, the air heater can be rotated in a counterclockwise direction. This will cause the secondary air to be heated more, and the primary air to be heated less. Thus it is possible to keep the air heating system operating at close to its optimum efficiency, because a lesser amount of cool air will have to be by-passed around air heater 24 through duct 23, even with changes in the moisture content of the coal being burned in the associated steam generator 10.

What is claimed is:

l. A rotary regenerative heater having a rotor of circular cross section rotatable about its central axis, said rotor having a plurality of equi-spaced imperforate radial partitions extending outwardly to the circumference of the rotor and forming a plurality of sectorial shaped portions therein, heat exchange surfaces positioned in each sectorial shaped portion, a cylindrical housing surrounding the rotor, a first duct having a sectorial shaped outlet for introducing heating gases to a first portion of the rotor at one end thereof, a second duct having a sectorial shaped inlet for receiving gases flowing from the first portion of the rotor at its other end, a third duct having a sectorial shaped outlet for introducing gases to be heated to a second portion of the rotor at said other end, a fourth duct having a sectorial shaped inlet for receiving gases flowing from the second portion of the rotor at said one end, a fifth duct having a sectorial shaped outlet for introducing gases to be heated in a third portion of the rotor at said other end, a sixth duct having a sectorial shaped inlet for receiving gases flowing from the third portion of the rotor at said one end, means for rotating the rotor in one direction, and means for rotating the rotor in the other direction, whereby the gases flowing to the fourth duct are hotter than the gases flowing to the sixth duct when the rotor is rotated in said one direction, and the gases flowing to the fourth duct are cooler than the gases flowing to the sixth duct when the rotor is rotated in said other direction.

2. The combination set forth in claim 1, including a furnace, primary air inlet ports for the furnace, secondary air inlet ports for the furance, the fourth duct is connected to the primary air inlet ports, and the sixth duct is connected to the secondary air inlet ports. 

1. A rotary regenerative heater having a rotor of circular cross section rotatable about its central axis, said rotor having a plurality of equi-spaced imperforate radial partitions extending outwardly to the circumference of the rotor and forming a plurality of sectorial shaped portions therein, heat exchange surfaces positionEd in each sectorial shaped portion, a cylindrical housing surrounding the rotor, a first duct having a sectorial shaped outlet for introducing heating gases to a first portion of the rotor at one end thereof, a second duct having a sectorial shaped inlet for receiving gases flowing from the first portion of the rotor at its other end, a third duct having a sectorial shaped outlet for introducing gases to be heated to a second portion of the rotor at said other end, a fourth duct having a sectorial shaped inlet for receiving gases flowing from the second portion of the rotor at said one end, a fifth duct having a sectorial shaped outlet for introducing gases to be heated in a third portion of the rotor at said other end, a sixth duct having a sectorial shaped inlet for receiving gases flowing from the third portion of the rotor at said one end, means for rotating the rotor in one direction, and means for rotating the rotor in the other direction, whereby the gases flowing to the fourth duct are hotter than the gases flowing to the sixth duct when the rotor is rotated in said one direction, and the gases flowing to the fourth duct are cooler than the gases flowing to the sixth duct when the rotor is rotated in said other direction.
 2. The combination set forth in claim 1, including a furnace, primary air inlet ports for the furnace, secondary air inlet ports for the furance, the fourth duct is connected to the primary air inlet ports, and the sixth duct is connected to the secondary air inlet ports. 